Report useful file names and line numbers from run_multiple_progs().

Report useful file names and line numbers from run_multiple_progs().

Previously if tests in run_multiple_progs() failed the report gave the file
name and line number of the ok() call in run_multiple_progs(). Now, where
possible, report the file and line of the actual test program. If this
information isn't available, report the error at the file and line which
called run_multiple_progs().

This will improve error reporting from lib/charnames.t, lib/feature.t,
lib/strict.t, lib/subs.t, lib/warnings.t and t/lib/croak.t